Label printing and/or labeling typically consists of label media which include an adhesive composition layer that is constantly and consistently tacky. Many of these label media are formed with a removable non-stick layer, containing a release coat and a release liner, over the adhesive composition layer, to prevent the adhesive composition layer from coming into contact with internal components of a label printer, applicator, or labeler and/or the printable layer of an adhesive sheet when an adhesive sheet is wound in a form such as a roll.
In some instances, the liner layer is disposed of after printing or at the time the label is applied to an article, either manually or by an autonomous process designed for the removal purpose. The disposable liner layers create waste disposal issues.
In other instances, an adhesive label is formed by a sheet, having a printed layer, a release coat, and an adhesive composition layer. The release coat prevents the adhesive composition layer from adhering to the printed layer, but standard printing, labeling, and label applying equipment must be coated with a non-stick material to prevent the adhesive composition layer of the adhesive label from gumming or jamming the equipment components. Instead of covering an adhesive composition layer with a non-stick material, a printable layer of a label and internal components of a label printer are coated with a non-stick material to resist the adhesive composition layer of the label that is constantly and consistently tacky. This technique requires the additional step of coating components with a non-stick material, which can significantly increase costs.
Numerous attempts have been made to use conventional polymeric adhesive compositions with tacky or pressure-sensitive adhesives (PSA) in liner-free label constructions where a non-stick or release layer is coated onto the opposite side of the adhesive label. These are not compatible in conventional labeling equipment, requiring special liner-free label printers and application systems. In addition, the non-stick top-coating greatly reduces the printability of the label. The PSAs cause machine problems by gumming up label application systems and create cleanup issues. Other attempts have been made to make a dry-gum or water or solvent or co-solvent remoistenable adhesive label. These are typically based on both carbohydrate and synthetic polymeric adhesives. These adhesives have little utility on many synthetic and non-porous substrates as they do not form substantial adhesive or mechanical bonds to the substrate. These substrates are labels prone to “swimming” or moving from the desired application area during down-stream processing due to a lack in rapid bond formation. As such, these attempts have had little success.
Certain liner-free labels have been developed having a printed layer, a sheet, and an adhesive composition layer that can be made tacky by an activator prior to or after printing/applying an image. However, many of these embodiments still require a non-stick coating to avoid the gumming problem discussed above, such as described in U.S. Pat. No. 6,298,894 by Nagamoto et al. which disclose the use of silicone oil as a non-stick coating. In addition, many of the activatable adhesive liner-free labels are water activated and/or solvent activated. These labels lack both strong adhesion on polymeric substrates and quick tack to polymeric substrates. These labels are also prone to “swimming” as discussed above.
U.S. Pat. No. 7,943,714 describes adhesive formulations. The polymers used in the formulations having a high acid number, e.g., 100 or greater. In the examples, the polymer solutions have a pH of 4 or less. Such highly acidic materials can be problematic. For example, hydrophobic polymers, which are typically formulated as emulsions, can be stabilized at low pH. Moreover, polymers with high acid numbers are prone to crosslink. Crosslinking can create a material that resists penetration of the activation fluid which can adversely affect performance, such as quick tack and/or long term adhesion.
Each of the prior art systems discussed above presents different drawbacks. A non-stick liner layer is typically non-recyclable and not re-usable, thereby generating waste for every label that is used. Coating components with non-stick material increases the costs of the system and may not entirely prevent gumming of the system, which is likely to occur when an adhesive residue adheres to the label printer/applicator component.
It is therefore desirable to eliminate the need for an adhesive sheet to be formed with a non-stick liner layer or for the label printer/applicator components to be coated with non-stick materials. It is also desirable for a water-activated and/or solvent-activated liner-free label to exhibit both quick tack to polymeric substrates and strong adhesion on polymeric substrates.
Accordingly, it is an object of the invention to provide liner-free adhesive labels and methods of making and using thereof, wherein the label is activated by water and/or another solvent and exhibits quick tack to, and strong adhesion on, a variety of substrates including polymeric substrates.
The compositions, methods, and kits described herein offer significant ecological benefits compared to the prior art as well as products currently commercialized in particular markets. For example, the compositions, methods, and kits described herein eliminate the liner backing which is a waste byproduct of liner-backed pressure sensitive adhesive labels. This reduces landfill waste and eliminates the energy and carbon emissions from the production of liner backing and the shipment of the material to suppliers and customers.
In addition, the compositions, methods, and kits described herein eliminate the silicone release layer which is either disposed of on the liner backing in liner-backed pressure sensitive adhesive labels or on the top of the printed layer of linerless pressure sensitive adhesive labels. In either existing art, the silicone presents an energy intensive manufacturing process and the addition of a petrochemical derivative product that is unnecessary and eliminated by the compositions, methods, and kits described herein, thereby reducing the carbon footprint of the label and the requirement for silicone to be utilized in the label manufacturing process.